Thermal compressor

ABSTRACT

The subject of this invention is a thermally actuated, vapordriven diaphragm pump wherein condition sensor means and cascaded condenser/heat exchanger means are employed to maximize the cycle rate of the pump and to minimize the amount of driving energy dissipated, thereby producing a pump of high efficiency.

United States Patent Inventor Herbert H. Saxe Owings Mills, Md. Appl.No. 886,167 Filed Dec. I8, 1969 Patented Sept. 14, 1971 Assignee TheBendix Corporation Continuation-impart of application Ser. No. 749,445,Aug. l, 1968, now abandoned.

THERMAL COMPRESSOR l l Claims, 5 Drawing Figs.

U.S. CI 417/339, 60/25 lnt. Cl ..F04b l7/00, F03g 7/06 Field of Searchl03/l 52,

References Cited UNITED sTATEs PATENTS 2,212,281 8/1940 Unsmmd no3/152x2,653,552 9/1953 Geel/aen.. :o3/152 2,673,525 3/1954 Lucas 1oz/1522,867,974 H1959 wenander 60/25 3,037,438 4/1963 ciesidski loa/255Primary Examiner-Robert M. Walker Attorneys-Plante, Arens, Hartz, Smith& Thompson, Bruce L. Lamb and William G. Christoforo ABSTRACT: Thesubject of this invention is a thermally actuated, vapor-drivendiaphragm pump wherein condition sensor means and cascadedcondenser/heat exchanger means are employed to maximize the cycle rateof the pump and to minimize the amount of driving energy dissipated,thereby producing a pump of high efficiency.

BOILER HEATER snm 1 or 2 FIG..1

BOILER HEATER INVENTOR HERBERT H. SAXE TORNEYS PATENTED SEP1 419mPATENTEU SEPMIQYI 3,604,822

SHEEI 2 UF 2 FIG. 2

vNvENToR HERBERT H. SAXE RTTORNEYS THERMAL COMPRESSOR This applicationis a continuation-impart of application Ser. No. 749,445, filed Aug. l,1968 now abandoned.

BACKGROUND OF THE INVENTION Diaphragm Pumps Diaphragm pumps have beenused in situations in which it is desired to isolate the fluid beingpumped from any portions of the pump mechanism which might be damaged byit. Common applications of this sort are for pumps for corrosive fluidssuch as acids, and abrasive fluids such as mud. Diaphragm pumps havealso been used in situations other than those noted above in which it isdesired that the fluid being pumped be maintained in a closed system. Afinal class of cases in which diaphragm pumps have been employed involveapplications in which the economy of manufacture or the recovery ofotherwise waste energy dictate the employment of diaphragm pumps insituations for which they are not otherwise particularly suited; thesesituations are characterized by the tolerability of poor pumpingeffectiveness.

Mechanically Actuated Diaphragm Pumps Mechanically actuated diaphragmpumps may be illustrated by U.S. Pat. No. 2,826,154 issued to A. C. Saxedisclosing a pump for pumping abrasive fluids, and U.S. Pats. No.3,250,225 and 3,391,644 issued to J. F. Taplin disclosingrolling-diaphragm-type pumps. It is apparent that in such mechanicallyactuated diaphragm pumps, the diaphragm excursion and pump cycling isdetermined by the length and speed of excursion of the drive rod orequivalent. Since this is the case, providing volumetric efficiency inthe operation of a mechanically actuated diaphragm pump is a simplematter of straightforward design. Volumetric efficiency is used hereinto refer to the condition in which the entire volume of a pump chamberis eective in pumping fluid. The highest vvolumetric efficiency occurswhen the entire chamber is filled with fluid to be pumped at thecompletion of the suction stroke, or downstroke, and is completelyevacuated of fluid to be pumped at the completion of the pumping orpower stroke.

The most commonly known mechanically actuated diaphragm pump is theautomotive fuel' pump, widely used because of its cost advantages.

Fluid-Actuated Diaphragm Pumps In fluid-actuated diaphragm pumps aworking fluid is employed as the immediate diaphragm-driving means. Insome fluid-actuated diaphragm pumps the driving fluid is anincompressible fluid which is metered to the pump-driving chamber inslugs of known volume by mechanical compressor means. In the case ofsuch pumps, securing efficient operation involves the sarneconsiderations as in mechanically actuated diaphragm pumps. One reasonfor using this type of pump in preference to the direct mechanicalactuating type is the convenience of having thernechanical-energy-supplying means located at some distance from thepump cylinder. Power may then be transmitted hydraulically to the pump.

Another case of fluid-operated diaphragm pumps are the so-calledproportioning pumps in which an additive fluid is pumped into a streamof a main fluid in a volume proportional to the volume of the main fluidflow. An example of this type of pump is found in U.S. Pat. No.3,294,031 issued to S. H. Latawic. It will be noted that the desideratumof a proportioning pump is the proportionality and not efficiency. InLatawics pump the main fluid is used to deform a first diaphragm whichin turn actuates mechanical means driving a second pump diaphragm.

A third class of fluid-actuated diaphragm pumps comprises those pumps inwhich the driving energy source is entirely fluidic and eicient pumpingis desired. In this class of pump the desired efficiency can only beobtained if some form of sensor means or cycling control meansresponsive in some manner to the diaphragm position is employed. Rayner,in U.S. Pat. No. 684,379, and Lucas in U.S. Pat. No. 2,673,525, teachmechanical valve control means directly connected to and directlyoperated by the diaphragm through a connecting rod which penetrates thepump cylinder. Hoenecke in U.S. Pat. No. 2,780,177 teaches control meanscomprising valves disposed through the pump cylinder wall and actuatedby the diaphragm. Geeraert in U.S. Pat. No. 2,653,552 teaches controlmeans comprising microswitches disposed through the pump cylinder walland actuated by the pump diaphragm. In sum, the prior art consists ofcontrol means which penetrate the pump cylinder, which is undesirable inmany applications, or pumps lacking control means which results in lesseicient operation.

Thermally Actuated Diaphragm Pumps ln order for a thennally actuateddiaphragm pump to operate efficiently, concern must be had not only forvolumetric eiciency, as in the other types of diaphragm pumps discussed,but also for thennal efciency. Prior thermally actuated diaphragm pumpsas illustrated in U.S. Pat. No. 2,212,281 issued to H. M. Ullstrand andU.S. Pat. No. 2,867,974 issued to H. S. Wenander are thermally ratherinefficient and are low in volumetric efficiency. In each of these casesachievement of volumetric efficiency is attempted by metering a knownvolume of volatile driving fluid to the boiler when it is desired tocommence the power stroke of the pump. The power stroke is thereforecompleted when the last of the fluid charge is boiled off. Volumetricefficiency can be provided in this manner only if the fluid being pumpedis under a precisely known pressure. Since in each case the fluid beingpumped communicates with atmospheric pressure which varies with altitudeand meterological conditions, the prior art pumps will in many cases beslow to recycle or will terminate the power stroke prior to thediaphragrns reaching its maximum excursion. It is further obvious thatpumps of this type cannot be at all volumetrically efficient insituations in which it is desired to pump fluids which may vary in feedpressure or viscosity. ln both the Ullstrand and the Wenander pump thedriving fluid is conveyed to the pump chamber by a conduit on whichcooling fins are mounted. At the completion of the power stroke thedriving fluid is condensed and returned to the boiler by the convectiveand radiative cooling action of the finned conduit. The thermalinefciency of such means is obvious; rst, the driving fluid is subjectedto cooling prior to being introduced into the pump chamber, and second,all of the energy which was supplied by the heating means, other thanthat which was actually used in propelling the pump diaphragm, isdissipated.

In addition, it will be noted that the shape of the pump chamber hasbeen uniformly viewed in the art as being a matter of convenience. Ithas, however, been further recognized in the art that diaphragm pumpshave an inherently high reliability resulting from the employment of asmaller number of moving parts than is typical in other types of pumps.While there is teaching in the an relating to increasing diaphragm lifeby oscillatory rather than fixed mounting of the diaphragm (see U.S.Pat. No. 3,124,078 issued to R. N. Hardy) and by carefully designing theshape of the diaphragm (see U.S. Pat. No. 3,062,153 issued to W, A.Losey), there has been no teaching in the art of the salutory effectupon diaphragm life of proper design ofthe shape of the pump chamber.

It is accordingly an object of the present invention to provide athermally actuated diaphragm pump having improved thermal and volumetricefficiency.

It is a further objective of the present invention to provide such apump wherein diaphragm life is extended with minimal sacrifice ofeffective pumping volume by improved design of the pump chamber.

Another object of this invention is to provide a thermally actuateddiaphragm pump employing sensor and control means responsive to theposition of the diaphragm within the pump chamber for eiciently cyclingthe pump.

mally actuated diaphragm pump which is capable of pumping substantialvolumes of fluid athigh pressure while producing very little operatingnoise.

These and'other objects,features and advantagesY of the invention willappear from the following description and appended claims when read inview of the accompanying drawings.

Briefly, the invention is embodied in a thermally actuated diaphragmpump in which a driving fluid is continuously boiled; the resultingvapor is applied to a main pump chamber to produce the pumping stroke ofthe pump diaphragm. The main pump chamber is maintained continuously atoperating temperature--approximately 250 F. The return stroke of thediaphragm is powered by avacuum produced in the main pump chamberbycondensation of the driving fluid in a secondary cooling system. Likethe boiler, the secondary cooling system runs continuously. Connectionof the main pump chamber to the sources of hot high-pressure vapor andvacuum is accomplished by latching solenoid valves. Means are providedto so actuate the valves that efficient pumping is obtained. The drivingfluid which is condensed in the secondary cooling system is returned tothe boiler by a transfer pump which is operated from the same sources ofhigh pressure and vacuum as is the main pump.

IN THE DRAWINGS FIG. 1 is a partially sectional view of a preferredembodiment of the inventive system employing a rolling diaphragm in acylindrical pump chamber.

FIG. 2 is a sectional view of an alternative shape for the pump chamberand the diaphragm.

FIG. 3 illustrates an alternative embodiment in which th heater elementis located within the boiler.

FIG. 4 is an elevation detail of one of the cooling fins employed in thecondenser of the secondary cooling system.

FIG. 5 illustrates an alternative embodiment of the main pump chamber inwhich the shape of said chamber maximizes the life of the diaphragm.

The invention as illustrated in FIG. l comprises the pump chamber l,which communicates by conduit 9 to valve 61 which alternately connectsthe chamber l to conduit 10 communicating with a source of highpressure, boiler 90, and conduit 1 l communicating with a source ofvacuum generated by the secondary cooling system 50, which comprises acondenser 59 and a closed circuit heat exchanger including coil 52.Chamber l also communicates with the fluid to be pumped by means ofconduits 4 and 5 and check valves 7 and 8. The driving fluid iscondensed in condenser 59 of secondary cooling system 50 and isdelivered by conduit 43, check valve 17, and conduit 14 to the workingchamber of a transfer pump 60. The transfer pump is operated from thesame high-pressure and vacuum sources as is the main pump. The transferpump 60 communicates with the sources of high pressure and vacuumthrough conduit 19 and valve 62 which alternately connects conduits 12and 13 to conduit I9. The condensed driving fluid is expelled from thetransfer pump under elevated diaphragm on the return stroke. Whendiaphragm 6 has l the energy losses which would inhere in the cycling ofthese elements and by economizer 4l whereby the condensed driving fluidprecools the vapor input to secondary cooling system 50 and is itselfpreheated prior to its return to boiler 90. Ener-l gy loss at main pumpchamber 1 is minimized by optional heating means 98 and insulation 99which will be more fully discussed later. Thermal and volumetrice'rciency are limproved by control means to be discussed in detail laterwhich control valves 61 and 62 to provide optimum cycling ofinterconnection to the high-'pressure and vacuum sources.

Having described generally the operation of the system, we turn now t'oa detailed description of its elements. Main pump chamber 1 comprises apair of symmetrical chamber wall members 2 and 3 having outwardly turnedflanges, a flexible y pump diaphragm 6 securely fastened at itsperiphery between the flanges by an integral ridge 100, the ,assembly ofthe chamber and diaphragm being fastened at the flanges by conventionalmeans, such as clamps or bolts, not shown. Member 2 contains a portcommunicating with driving fluid conduit 9. Member 3 contains a portscommunicating with conduits 4 and 5 for inlet and outlet, respectively,of the fluid to be pumped, controlled respectively by check valves 7 and8. In the embodiment illustrated in FIG. 1 elements' 2 and 3 arecylindrical segments fabricated from nonmagnetic stainless steel. Otherconvenient materials, however, can be used, and other shapes may beemployed as will be more fully disclosed later. In the embodiment ofFIG. 1 the diaphragm 6 is a cylindrical rolling diaphragm. Securelyattached to the diaphragm 6 is a small permanent magnet 8l. lf desired,an electrical heating element 98 may surround the pump chamber. The pumpchamber and the electrical heating element, if used, is sheathed intherrnal-insulating material 99. The purpose of the heating andinsulating elements is to maintain the pump chamber at a constanttemperature above 250 Fahrenheit to prevent dissipation of the energy ofthe hot high-pressure vapor. lf electrical power is convenientlyavailable at the location at which the pump is to be used, theelectricalfheating means 98 may be employed to preheat the pump chamberto operating temperature. If the use of the electrical heating means isinconvenient, the entering vapor will be used to heat the cylinder andthermal equilibrium and efficiency will not be achieved until the thirdor fourth pumping stroke. The cycling control system comprises tenninals71 and 73 between which an electricalpotential difference is maintained,latching solenoid-controlled valve 6I, controlsolenoids 67 and 68, andreed switches 63 and 64. Reed switch 63 is located on the outer surfaceof the chamber structure at a point corresponding to the maximum travelof the pump diaphragm on the power stroke. Reed switch 64 is similarlylocated in a position corresponding to the point of maximum travel lofthe pump reached the end of its power stroke, magnet 81 causes thecontacts of reed switch 63 to close completing an electric circuit fromterminal 71 through reed switch 63 and solenoid 68 to terminal 73,thereby causing current to flow in solenoid 68 which in turn causessolenoid-controlled valve 61 to connect the pump chamber to the sourceof vacuum through conduits 9 and l1. The downstroke of diaphragm 6 thencommences. The current flow between terminals 71 and 73 is of very briefduration since the downstroke of the diaphragm immediately removesmagnet 81 from active relationship with reed switch 63. Valve 6l howeveris latched into the downstroke position. At the completion of thedownstroke magnetSl closes reed switch 64 causing valve 61 to againconnect the pump chamber to the source of high pressure through conduits9 and l0, thereby commencing the next power stroke. A. similar controlsystem is employed at the transfer pump 60. Ihe transfer pump controlsystem comprises terminals 72 and 74, solenoidsv 69 and 70, reedswitches 65 and 66, permanent magnet 82 and solenoid-controlled latchingvalve 62. Valves 61v and 62I are shown as three-way solenoid-controlledvalves. An obvious alternative, if desired, would be to utilize two-waysolenoid-controlled valves in each of conduits l0, l1, l2 and 13 with aconduit T-connection between conduits 9, and 11, and 12, 13 and 19. Itcan be seen that the control systems would function identically with thealternative valving. When the fluid to be pumped is of known constantpressure and viscosity, magnets 81 and 82 and reed switches 63, 64, 65and 66 may be replaced by ratio timers set to so energize the solenoidsas to provide efficient cycling.

Transfer pump 60 comprises wall members 24, 32 and 33, and diaphragrns16 and 20, which wall and diaphragm members are securely fastenedtogether at 101 and 102 similarly to the main pump chamber at 100.Diaphragm 20 is the driving diaphragm and diaphragm 16 is the pumpingdiaphragm. Diaphragms 16 and 20 are connected by suitable means at 22and 23, respectively, to a rigid rod member 21, whereby motion impartedto diaphragm 20 by alternate application of high pressure and vacuum istransmitted to diaphragm 16 which performs the pumping ofthe condenseddriving fluid.

The secondary cooling system 50 is a separate self`-con tained fluidcircuit in which coolant circulation is achieved by a combination ofvapor pressure and gravity feed. The system comprises shell and tubecondenser 59 and a heat exchanger composed of coil 52 and radiator vanes51. Ifelectric power is available, and if desired, a fan 53 may be usedto provide forced air cooling at the heat exchanger. Forced air cooling,however, is not required for efficient operation of the secondarycooling system. The cooling system is charged with a coolant such asFreon l2 which will exist in mixed liquid and vapor state at ambienttemperature. ln the quiescent state gravity will cause the liquidcoolant to be located in the condenser tube 58 and the vapor-statecoolant in the heat exchanger coil 52. When valve 61 or 62 connects itsassociated pump chamber with conduit l1 or 13, respectively, the hotvapor from the pump chamber is brought through economizer 41 and conduit44 into contact with the cool vanes 57 of the condenser. 0n contact withthe vanes the vapor is condensed thereby creating a vacuum operatingupon diaphragm 6 or diaphragm 20, as the case may be, to provide apowered downstroke for said diaphragm. The heat transferred from thedriving vapor to the vanes 57 causes the secondary coolant in tube 58 toboil. Initially, the vapor produced by this boiling proceeds under vaporpressure by conduits 54 and 55 to the heat exchanger coil 52. The vaporis condensed in the heat exchanger, however, and the liquid coolant isreturned under gravitational influence to cooling tube 58 by conduit 54.The presence of liquid coolant in conduit $4 then prohibits the vaporboiled off in tube 58 from entering conduit 54 ad all vaporizedsecondary coolant proceeds to the heat exchanger through conduit 55. Atthis point the forces of vapor pressure and gravitation reinforce eachother in maintaining circulation of the secondary coolant. The condenseddriving fluid is fed under gravitational influence from condenser 59through conduit 43 to check valve 17 and thence to the transfer pumppumping chamber.

FIG. 2 illustrates an alternative embodiment of the main pump chamber inwhich members 2' and 3' corresponding to members 2 and 3 of FIG. 1respectively define a spherical or cylindrical pump chamber, and 6'corresponding to 6 of FIG. l is a flat diaphragm as opposed to therolling diaphragm of FIG. 1. The other primed numbers of FIG. 2correspond to their unprimed equivalents of FIG. l.

FIG. 3 shows a section 90' of the boiler corresponding to boiler 90 ofFIG. l and a heater 92 disposed within boiler 90. While heater 91 ofFIG. 1 may be any convenient type of heater, electrical, chemical ornuclear, the embodiment of FIG. 3 is best adapted to use with a nuclearheater 92. Since the heating means 98 and the fan 53 Shown in the systemin FIG. 1 are optional elements and are not necessary for the operationof the system and since control currents flow from terminal 71 to 73 and72 to 74 for only very short periods of time, a pump adapted forcontinuous operation for long periods of time in inaccessible locations,such as under sea or on the lunar surface, may be provided by usingnuclear heater 92 in the boiler and long-life batteries for valveoperation.

With reference now to FIG. 5, another aspect of this invention relatesto extending the life of the pump diaphragm. This is especially usefulin conditions in which long continuous untended operation is desired asdiscussed above. The life of the pump diaphragm is inverselyproportional to the stress to which said diaphragm is subjected at itsHex points. Minimum stress is provided by having a short stroke.However, this provides very small pumping volume. The modification ofFIG. 5 relates to optimization of the competing factors of maximumpumping volume and minimum diaphragm stress. The main pump chamberillustrated in FIG. 5 is an embodiment of the invention whereindouble-prime numbers refer to functionally equivalent parts to thoseshown unprimed in FIG. l. For any given pumping volume desired, thestress upon the diaphragm is minimized by the use of a paraboloidal mainpump chamber.

The invention claimed is:

1. A fluid pump comprising in combination:

a chamber having fluid inlet and outlet ports at one end, a drivingfluid port at the other end, a flexible diaphragm disposed within saidchamber whereby communication of fluid between said ports at oppositeends of said chamber is prevented and whereby the volume of said chambermay be made to communicate substantially entirely with said inlet andoutlet ports or substantially entirely with said driving fluid port;

a source of high pressure including a heater, a volatile driving fluid,and a boiler;

a source of vacuum including a cooling system;

valve means for alternately connecting said driving fluid port to saidsource of high pressure and to said source of vacuum;

means applied at said chamber for preventing dissipation of thermalenergy therefrom; and

means responsive to the position of said diaphragm for actuating saidvalve means.

2. A fluid pump comprising in combination:

a'chamber having fluid inlet and outlet ports at one end, a

driving fluid port at the other end, a flexible diaphragm disposedwithin said chamber whereby communication of fluid between said ports atopposite ends of saidchamber is prevented, and whereby the volume ofsaid' chamber may be made to communicate substantially entirely withsaid inlet and outlet ports or substantially entiifely with said drivingfluid port; a source of high pressure including a heater, a volatiledriving fluid, and a boiler; a source of vacuum including a coolingsystem densing driving fluid admitted therein; valve means foralternately connecting said driving fluid j port to said source of highpressure and to said source of vacuum; means applied at said chamber forpreventing dissipation of thermal energy therefrom; means whollyexternal to said chamber for actuati 4g said valve means; and

a transfer pump having inlet and outlet ports for conveying thecondensed driving fluid from said boiler.

3. The fluid pump of claim 2 wherein said cooling jsystem comprises:

a shell and tube condenser, theshell of said shell and tube condenserhaving inlet and outlet ports for the dving fluid to be condensed, saidinlet port communicating with said valve means, said outlet portcommunicating with an inlet port of said transfer pump; coil and vaneheat exchanger communicating with the tube of said shell and tubecondenser, said tube and said coil forming a closed fluid circuit;coolant fluid within said closed fluid circuit, said heat exchangerbeing disposed above said condenser whereby said coolant fluidcirculates in said closed fluid circuit by cooperating forces ofgravitation and vapor pressure; and a plurality of cooling fins disposedwithin said condenser in thermally conductive relation with said tube ofsaid condenser.

for con-

1. A fluid pump comprising in combination: a chamber having fluid inletand outlet ports at one end, a driving fluid port at the other end, aflexible diaphragm disposed within said chamber whereby communication offluid between said ports at opposite ends of said chamber is preventedand whereby the volume of said chamber may be made to communicatesubstantially entirely with said inlet and outlet ports or substantiallyentirely with said driving fluid port; a source of high pressureincluding a heater, a volatile driving fluid, and a boiler; a source ofvacuum including a cooling system; valve means for alternatelyconnecting said driving fluid port to said source of high pressure andto said source of vacuum; means applied at said chamber for preventingdissipation of thermal energy therefrom; and means responsive to theposition of said diaphragm for actuating said valve means.
 2. A fluidpump comprising in combination: a chamber having fluid inlet and outletports at one end, a driving fluid port at the other end, a flexiblediaphragm disposed within said chamber whereby communication of fluidbetween said ports at opposite ends of said chamber is prevented, andwhereby the volume of said chamber may be made to communicatesubstantially entirely with said inlet and outlet ports or substantiallyentirely with said driving fluid port; A source of high pressureincluding a heater, a volatile driving fluid, and a boiler; a source ofvacuum including a cooling system for condensing driving fluid admittedtherein; valve means for alternately connecting said driving fluid portto said source of high pressure and to said source of vacuum; meansapplied at said chamber for preventing dissipation of thermal energytherefrom; means wholly external to said chamber for actuating saidvalve means; and a transfer pump having inlet and outlet ports forconveying the condensed driving fluid from said boiler.
 3. The fluidpump of claim 2 wherein said cooling system comprises: a shell and tubecondenser, the shell of said shell and tube condenser having inlet andoutlet ports for the driving fluid to be condensed, said inlet portcommunicating with said valve means, said outlet port communicating withan inlet port of said transfer pump; a coil and vane heat exchangercommunicating with the tube of said shell and tube condenser, said tubeand said coil forming a closed fluid circuit; a coolant fluid withinsaid closed fluid circuit, said heat exchanger being disposed above saidcondenser whereby said coolant fluid circulates in said closed fluidcircuit by cooperating forces of gravitation and vapor pressure; and aplurality of cooling fins disposed within said condenser in thermallyconductive relation with said tube of said condenser.
 4. The fluid pumpof claim 2 with additionally a heat exchanger interposed between saidvacuum source and said boiler for transferring heat from driving fluidexhausted from said chamber to driving fluid condensate entering saidboiler.
 5. The fluid pump of claim 2 wherein said means applied at saidchamber for preventing dissipation of thermal energy therefromcomprises: a jacket of thermal-insulating material conformablysurrounding said chamber, said jacket having holes permitting saiddriving fluid port and said fluid inlet and outlet ports to communicatewith said chamber.
 6. The fluid pump as claimed in claim 5 withadditionally an electrical heating element disposed on the inner surfaceof said jacket, said heating element substantially surrounding saidchamber.
 7. The fluid pump of claim 2 wherein said transfer pumpcomprises: a working chamber having fluid inlet and outlet ports and afirst flexible diaphragm disposed within said working chamber; a drivingchamber having a driving fluid port and a second flexible diaphragmdisposed within said driving chamber; valve means for alternatelyconnecting said driving fluid port to said source of high pressure andto said source of vacuum; and a rigid rod member connected at one end tosaid first flexible diaphragm and connected at the other end to saidsecond flexible diaphragm.
 8. The fluid pump of claim 2 wherein saidvalve means are solenoid-actuated latching valves and said means whollyexternal to said chamber for actuating said valve means is a ratiotimer.
 9. The fluid pump of claim 2 including additionally: means whollywithin said chamber and attached to said diaphragm for controlling saidmeans wholly external to said chamber for actuating said valve means,whereby said means wholly external to said chamber is made responsive tothe position of said diaphragm within said chamber.
 10. The fluid pumpas claimed in claim 9 wherein: said means wholly within said chamber isa permanent magnet; said valve means are solenoid-actuated latchingvalves; and said means wholly external to said chamber for actuatingsaid valve means includes a first reed switch adjacent to said chamberat a point corresponding to a first extreme of travel of said diaphragm,and a second reed switch adjacent to said chamber at a pointcorresponding to a second opposite extreme of travel of said diaphragm.11. The fluid pump as claimed in claim 10 wherein said heater is anuclear heater and is disposed within said boiler.